Field of the Invention
The present invention relates to electrical power cables. More specifically the invention relates to a flexible and watertight metallic water barrier for a submarine power cable.
Description of Related Art
Submarine cables applied for different purposes are well known in the art. Such cables are exposed to harsh environments that may cause damage to the cables if they are not sufficiently protected against water ingress and mechanical force or pressure loads.
Different types of submarine cables exist, e.g. cables for carrying signals and cables for carrying high voltages. Electrical high voltage cables are categorized as medium, high and extra high voltage (MV, MH, EHV) power cables. They are typically designed with a cable core enclosed by a metal sheath making a water tight metallic barrier as well as an outer sheath made in for instance polyethylene (PE). The metal sheath is typically corrugated copper or aluminum sheath and solid copper or aluminum sheath. Submarine cables are used for different applications. Some cables are used for static applications while others are used for dynamic applications.
The present invention belongs to the latter category of power cables, i.e. a power cable that is designed to be used for dynamic applications. An example of a dynamic application is a cable installed on a floating offshore installation. The cable will then be exposed to dynamic forces.
One problem with submarine power cables with metal sheath used for dynamic applications is that they are stiff and vulnerable to movements resulting in poor fatigue properties.
A cable that is constantly moving and exposed external dynamic forces will at some point experience possible fatigue fracture on the outer sheath resulting in possible water ingress in the cable.
Said metal sheath will protect a cable from water ingress, but will make the cable less flexible and thus less usable for dynamic applications. There are however several solutions for making a submarine power cable more flexible while keeping the watertight metallic barrier.
EP-0213946 A2 describes an electrical power cable with a shielding tape with a conductive metal layer on one side. The metal layer has convolutions with a water blocking material. This construction will protect the inner core from water ingress, but the cable will have degraded flexibility, and as mentioned flexibility is an important factor when used in dynamic installations.
High voltage cables comprising a metallic barrier and having good flexible properties for application in dynamic installations have been a big issue and challenge for cable manufactures.
There is a need for a cable that is both watertight and flexible and thus less prone to fatigue.
The present invention has been realized in order to overcome weaknesses with prior art by providing a watertight metallic barrier for a submarine power cable having good flexibility.